Letterman announced that he was retiring from the Late Show after serving as its host for 21 years on Thursday, making it official on Thursday night's show. "I just want to reiterate my thanks for the support from the network, all of the people who have worked here, all of the people in the theater, all the people on the staff, everybody at home, thank you very much," he told the audience.

And in a preview from tonight's episode, Letterman, who is the longest-running host in late-night history, reveals why he decided to call it quits!

"A couple of days ago, Jane, a lovely woman who does my makeup every night—and you think you got a lousy job," Letterman jokingly explains to Paul Shaffer, his longtime sidekick and musical director, in the clip above. "She says to me, ‘Dave, there's really nothing more I can do. I said, ‘OK, fair enough.'"

Letterman, 66, also opens up about his plans for life after leaving the Late Show in 2015, telling the audience, "A year from now, I'll be on a beach with a metal detector!"

You earned it, Letterman!

Tonight's guest Billy Crystal also pops up in the clip to react to the sad news of Letterman's retirement. Tissues and tears are involved!